| Re: [eigen] Nesting by reference of by value ? |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Nesting by reference of by value ?
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Wed, 18 Nov 2009 12:45:54 -0500
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2009/11/18 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
>
> Hi,
>
> I've just played a bit with Hauke's nesting refactoring fork
> (https://bitbucket.org/hauke/nesting-refactoring/).
>
> Let me recall that currently expressions are nested by reference that
> enforces the use NestByValue when a function has to return a nested
> expression. See for instance adjoint() which returns
> Transpose<NestByValue<CwiseUnaryOp<ei_scalar_conjugate<Scalar>, Derived> >
>>. As you can see this is pretty annoying. In Hauke's fork lightweight
> expressions (i.e., all but Matrix) are automatically nested by value. So
> need for the NestByValue workaround.
>
> So now the question is what about the performances ? Well I tried a very
> simple example:
>
> Vector4f a, b, c, d;
> c = a+b+c+d;
>
> and here are the respective assembly codes generated by g++ 4.3.3
That wouldn't be the first time that g++ 4.3 is stupid, right?
It would be interesting to see g++ 4.4.
Benoit